Levulinic acid esters are known to be useful as plasticizers or solvents as well as in the preparation of free levulinic acid by the hydrolysis of the ester. Levulinic acid is useful as a food-flavoring agent as well as an intermediate in the preparation of a variety of chemicals for industrial and pharmaceutical uses such as, for example, in the production of diphenolic acid, a component of protective and decorative finishes and in the preparation of calcium levulinate, a particularly suitable form of calcium for intravenous injection. The degree of actual commercial use of levulinic acid and its esters has nevertheless been rather limited because the available methods of preparation of the acid and the esters are not very practical from a commercial point of view since the yields have been rather low and the cost is relatively high.
The basic method for preparing levulinic acid esters is disclosed in U.S. Pat. No. 2,763,665 and British Pat. No. 735,693. This method comprises heating furfuryl alcohol at a temperature of 64.degree. C. to 220.degree. C. with a different alcohol under substantially anhydrous conditions with agitation in the presence of a catalyst such as hydrogen chloride or hydrogen bromide. It is important to maintain the concentration of furfuryl alcohol in the reaction mixture below 2% by volume of the other alcohol. The other alcohol is used in the amount of at least 4 molecular portions per molecular portion of furfuryl alcohol. U.S. Pat. No. 3,203,964 discloses an improvement of said process by incorporating in the reaction mixture a small amount of water, and also preferably premixing furfuryl alcohol with a portion of the other alcohol prior to the addition of furfuryl alcohol to the reaction mixture. It is said that in this process the other alcohol can be used in amounts as low as 2 mols of the other alcohol per mol of furfuryl alcohol. Finally, British Pat. No. 1,283,185 discloses a further modification of the basic process which comprises heating furfuryl alcohol in water with either hydrochloric or oxalic acid catalysts and in the presence of at least one mol of a water-soluble aliphatic ketone per mole of furfuryl alcohol.